The present invention relates to a rotary recording medium having a guide track and recording and reproducing apparatus which records and reproduce information on and from the rotary recording medium.
Conventionally proposed are optical disk apparatus that perform the recording of information by forming pits by irradiating a laser beam to a rotating rotary recording medium (hereinafter referred to an optical disk), and that perform reproduction of information by irradiating the optical disk with a laser beam and using the reflected light to detect the presence or absence of pits.
In the conventional optical disk, a guide track is formed on a recording surface thereof. The guide track has one of a concentric shape and spiral shape with the center of rotation of the optical disk as the center. This guide track, for example, is constituted by a continuous groove (hereinafter referred to a guide groove) having a predetermined depth. Then, a spot of a main laser beam and the spots of two sub laser beams on either side are arranged in the direction of the radius of the optical disk and tracking control is performed so that the two sub laser beams scan end portions of the guide groove. Accordingly, when information is recorded the main laser beam accurately scans between the adjacent guide track turns and a recording track where information is recorded is formed. When information is reproduced, as in the case of the recording, sub laser beams are guided by the guide grooves and so the main beam accurately scans on the recording track.
The inventor of the invention of the present application has proposed, in U.S. patent application Ser. No. 426,789, a information signal recording and reproduction apparatus that enables the recording and reproduction of high density information by performing the recording and reproduction of two tracks at the same time as the two main laser beams.
However, in an apparatus that performs the recording and reproduction of two tracks simultaneously as described above, if tracking control is performed by providing two sub laser beams for the main laser beam as in the case of conventional apparatus, it is necessary to provide six laser beams. Accordingly, the optical pickup that includes the light source for the laser beams becomes large.